For more than ten years the application of Trichoderma fungi has been common practise in horticulture. They help cultivated crops grow better and become more resistance to diseases. How this symbiosis works is a complex area of research. Nevertheless the developments keep coming. This year a new strain is being launched on the market.
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Until recently, controlling aphids caused Christiaan Bot, production manager at Arend Roses in Maasland, a lot of headaches. Although he is familiar with biological methods, aphids were still treated with chemicals. However, the effectiveness of the chemicals was deteriorating rapidly, so Christiaan switched to the gall midge Aphidoletes, which turned out to be successful.
"Until two years ago, we used to spray against aphids about once a fortnight, but as time went on aphids reappeared more and more quickly. None of the chemicals currently permitted work well,” according to Christiaan. "In the past, I've tried to combat aphids biologically, sometimes using parasitic wasps (Aphidius). This worked well, but the problem with roses is that the aphid mummies were visible on the stem when the flowers were harvested. Although these mummies are entirely natural, it is perceived as a quality problem."
Marcel Verbeek, consultant at Biobest Netherlands, suggested to Christian that he should do a test with the Aphidoletes gall midge. This midge is a real predator, and leaves no mummies behind on stems. The experiment was successful. Marcel Verbeek says, "The trick is not just using the right natural predator; it is equally important to create the right conditions for this predator. It is crucial for Aphidoletes that it has the right environment to breed in."
Christiaan managed to create such an environment using buckets of moist coconut substrate, covered with old newspapers. This mimics the natural conditions which are necessary for adult mosquitoes to mate. They then go into the greenhouse looking for infestations of aphids.
Aphidoletes is known for its excellent searching ability. With just 20 buckets, Christiaan managed highly effective aphid treatment on 4 hectares of roses. That translates to just 0.2 individuals per square meter, which seems very little, but enough to give excellent results.
With Aphidoletes destroying aphids, Arend Roses now has a new, highly effective addition to its biological control measures. Christiaan says, "We had already managed efficient biological control of whiteflies, spider mites and thrips, but this is the first time we have found an effective natural remedy for aphids. Now we really have found the missing link for an integrated biological systematic approach."
Vegetable growers don’t like to admit that they have mealybug. A group of cooperating parties therefore sent a questionnaire to growers in 2015. From this it appears that mealybug is a tricky pest to control and it is becoming increasingly prevalent in vegetable production, especially in tomatoes, sweet peppers and eggplants. The method of control varies. A clear-cut biological strategy is still lacking. Various companies and research centres are now working on effective, affordable control methods.
Mealybugs live on plant sap and tend to live in colonies. Due to their uptake of so much sap plants can loose vigour. The pests often live on the fruit, in the axils of the stems or at the base of the plant. For example in sweet peppers they live under the crowns of the fruit and in tomatoes often initially at the base of the plant, in the clips and low on the stems.
Growers often overlook mealybugs because they hide themselves so well in plants axils or in the greenhouse construction to escape their natural enemies and/or difficult environmental conditions. Only during peak periods do they emerge on mass.
Males and females
Adult males and females differ greatly in appearance. Adult females are covered with a protective waxy layer, usually have legs, no wings and are 0.4 to 0.8 mm long. The sexually mature females produce a sex pheromone to attract males.
Fertilized females lay hundreds of eggs, usually in an egg sac that consists of a white fleecy mass. This protects the eggs from predators, pathogens, drought and excessively high air humidity. The eggs also hang more easily on the plants in these egg sacs. After laying the eggs the females dry out. Unfertilised females and fertilised females that are overwintering can survive for several months. Female mealybugs go through five developmental stages: eggs, three nymph stages and the adult stage. The optimal conditions for the development of mealybugs are 26ºC and 60% humidity. Each stage takes six to 16 days. Adult males are winged and are about 1 mm long. They don’t have any mouthparts and therefore cannot feed. They survive only a few days to mate. The males go through six development phases as they mature to the adult stage.
In 2015 Biobest and growers association LTO Glaskracht Nederland looked closely at the problem. They contacted growers and crop protection advisors and invited the growers via the organisation’s website to complete a questionnaire about their experiences with mealybugs and how they deal with the problem. In total 89 growers answered the questions of which 43 grew tomatoes, 25 sweet peppers, seven aubergine and seven cucumbers. In addition, they visited ten growers. Specimens were collected and identified by a European specialist at species level.
Two harmful species were identified: Pseudococcus viburni in sweet peppers, eggplant and tomato and Phenacoccus solani at a sweet pepper nursery.
P. viburni is the most common species found in Dutch greenhouse vegetable crops. This originates from neotropical areas. Under greenhouse conditions development takes one to two months. This species can easily survive the cold and overwinters mostly in the first nymph stage in bark or in the ground.
One pepper grower also discovered P. solani. It is the first time that it has been found in a Dutch greenhouse although this species is prevalent worldwide. It is a major pest in sweet peppers in Spain. At first glance it seems to be whiter than P. viburni. This type is polyphagous and can settle on more than 30 plant families. This mealybug develops in 15 to 33 days at a temperature between 20 and 30ºC.
Found year round
One of the questions was whether growers ever had or still have trouble with mealybugs. The survey showed that this pest occurs in the greenhouse the whole year round if its spread is not stopped in time. Just 40% of the growers who answered the survey managed to eradicate the pests. On a few nurseries the pests spread so much that it was impossible to bring them under control using the usual methods.
The problem is the greatest in tomatoes. Of the 43 participating growers 19 had suffered problems and it is was still present on 11 nurseries. Of those participating in the survey the area infected with mealybug rose from 7 ha in 2013 to 10 ha in 2015.
Infected plants return about 10% less. Growers certainly waste just as much money searching for and controlling the pest.
Good hygiene measures and identifying the problem on time remain the first steps of control. Growers appear to be very creative at identifying and monitoring the mealybug. They reduce the infection by steaming the sub-surface, burning the infected stems, and using insect glue on substrate slabs and the greenhouse structure.
Most growers control the problem locally. Growers that suffer problems year round blanket spray two or three times when the young plants arrive. On these nurseries new colonies continually appear even after the entire greenhouse has been disinfected. The females escape the control and hide in the greenhouse structure (often next to the meter cupboard). Young larvae, the crawlers, are immediately seen on the young plants.
Many growers use the neonicotinoids Calypso or Gazelle with strong wetting agents to improve the control. The mealybug hotspots are sprayed two to four times after each other with an interval of four to seven days, depending on the level of infection. The old hotspots are checked every four weeks.
Gap in a strategy
A clear biological control strategy is not yet available. The survey shows that experiences with biological pest control are still very limited and the introduction of natural enemies are often too late and carried out with too few predators. Vegetable growers prefer to use biological solutions to limit residue on their products, but this approach needs to be effective. Natural enemies and green pesticides will play an important role in an integrated approach in future.
Various researchers from companies and research institutes are working on the problem and hope to be able to offer effective and affordable methods to growers as soon as possible. Biobest is experimenting this year with predators. Larvae of Cryptolaemus (ladybirds) and lacewings seem to have potential. They can clean up the first hotspots, but the biological strategy has yet to be fine-tuned into affordable solutions for growers.
Several parasitic wasps have also been reported some of which are available commercially. However, these do not offer a solution in the short term.
Based on the survey, a literary review and practical experiences, it is meanwhile possible to provide advice on how to prevent the development of mealybug or to slow it down.
Spray the infected plants and contaminated areas before the change of crop three to four times with a neonicotinoid combined with a super wetting agent and/or remove infected plants and dispose of them in rubbish bags. Remove the old crop and plant remains. Disinfect the ground and substrate. Clean the entire greenhouse with formalin or hydrogen peroxide and disinfect materials. Renew the substrate annually. Properly inspect plant material when in arrives at the nursery.
2. Scouting and monitoring
Detect the first mealybug areas fast. The pests hide in crevices and cracks under cloths, slabs, gutters, gutter edges and between pipe rail supports and greenhouse pillars. Inform and instruct personnel. Mark the infected plants and contaminated trellis with tape. Use yellow sticky traps with sex pheromones to attract the males.
3. Physical control
Remove infected material; pick leaves (pick the stem bare). Spray with soap or an oil.
Control is a matter of patience, monitoring and persistence. The crawlers are easy to kill but the adult females are difficult to control with insecticides because of their protective waxy layer. For good, long-lasting control it is recommended to use a broad action substance that works against mealybug. Take note: this should not be used with natural predators. Substances with systemic activity via the plant sap are usually more effective. Spray frequently because the hot spots often return in the same place (blocks of three sprays with a 7 to 14 day interval, repeat after six weeks if necessary). Spray the stems well. Mealybugs often take cover in the axils. Use a wetting agent to ensure good contact with the pests and their waxy layer. Use a lot of water.
Mealybug is an increasing problem in greenhouse cultivation. A stocktake in 2015 highlighted two common types. Growers address the problem in various ways: hygiene, spraying, a mechanical approach (burning, glue, brushing away) and the use of natural predators. However, these control methods are not enough. Further research is being carried out.
Text: Marleen Arkesteijn, Juliette Pijnakker and Joke Vreugdenhil
Images: Marleen Arkesteijn and Biobest
Combating aphids with biological crop protection agents is everything but easy. This is why Biobest is involved in relentless research into new ways to get rid of aphids. The result? The hoverfly, Sphaerophoria rueppelli, is being deployed in the battle.
Many commercial crops are plagued by a plethora of aphid varieties that can create a tremendous amount of damage. A lot of preventive pest control strategies have already been explored. Many of these focus on the use of parasitoids. Although these are quite effective, they still aren’t effective enough to be truly reliable. According to Biobest, the biggest problem is that every parasitoid attacks only a limited number of hosts.
The latest weapon in the war against aphids, Sphaerophoria rueppelli, is a native species that is very common throughout Europe and in numerous Mediterranean countries. Its larvae are highly efficient predators of various ahipd vaieties, including Macrosiphum euphorbiae. Not only do hoverflies feast on aphids, they also consider whiteflies, thrips, and spider mites to be a delicacy. ‘Sphaerophoria rueppellii will go actively in search and fly long distances to detect even the first signs of an aphid colony,’ explains Yann Jacques, Product Manager for Macrobials at Biobest. ‘The Sphaerophoria System is therefore also a preventative system. It is a perfect complement to our existing range of parasitoids and predators.’
Adult hoverflies are virtually harmless, as they feed only on pollen and nectar. It’s the larvae, however, that are the leading players in the war against aphids. Adult females prefer to lay their oval-shaped greyish white eggs in large colonies of aphids, to ensure that their offspring will have plenty of nourishment. Each female can lay up to 20 eggs a day, and up to 400 eggs in all. The green larvae that are hatched can consume an average of 200 aphids during their larval stage, which lasts nine days at a temperature of 25°C. They will also feed on other pests, such as whiteflies, thrips, and spider mites. ‘What’s so interesting about this system is that the hoverflies can be deployed concurrently with aphid parasitoids. Hoverfly larvae will devour only the non-parasitised aphids. By deploying both, the number of aphids will be reduced even more dramatically,’ concludes Jacques. S. rueppellii is highly efficient when deployed in sweet pepper crops, but it looks as if this system will also promote aphid control substantially in other vegetable, fruit and decorative plant crops.
Bees and bumblebees are, thanks to their build and behaviour, good pollinators. But they have additional potential. They are also useful for disease control by transferring antagonistic microorganisms and for retrieving information about diseases in the fields. An important aspect for all these tasks is: How do we keep them working under the ‘new’ growing conditions in the greenhouse?
Sjef van der Steen, researcher in the department Bio Interactions and Plant Health at Plant Research International, Wageningen, the Netherlands, researched the additional possibilities for these pollinators such as in disease control and air quality detection.
His research considered two questions: Is crop protection via bees and bumblebees effective and is it safe for these creatures? He provided the bees with the antagonist Trichoderma that works against Botrytis. The bees introduced sufficient Trichoderma onto the plant to prevent it becoming diseased. The substance had no effect on bees and bumble bee families.
Exit and entry opening
Then he carried out exploratory research into possible ways to establish a system in which the incoming and outgoing flow of bees could be separated. He placed a small type of aquarium pump at the exit route that continually released fresh spores.
The principle was picked up and further developed by Biobest. Meyers Softfruit, of Riemst, Belgium, has been using this method for two years. The bumblebee hives are equipped with an entry and exit opening. A powder dispenser is integrated into the exit opening. When a bee flies away it automatically takes with it some of the fine powder to the leaves and flowers. It was first tried out with the biofungicide VerderaB4. This is the first substance that has been permitted for this application. This year Van der Steen will join on-going Dutch research in Bleiswijk once new antagonists have being selected.
During their flight back from the flower the bees carry with them not only pollen but also other ‘information’ such as bacteria and fungi which have carried by air into or onto the flower. By analysing which disease or pest is present it’s possible to take timely action before the symptoms become visible. In order to get a good picture of what exists, the researcher had to make a number of choices. Where to place the colony of bees? How many colonies do you need? How do you ensure that the bee colony flies to a certain crop?
The next step was to take samples. He used two methods for obtaining the bacteria or fungi for analysis. “One method involves pulling the bees off the flight path, killing them and then immersing them. By using the other method the bees remain alive. We get them to walk through a tube containing a sticky material. Part of what they carried with them remains in the tube.” For both methods the researcher created a solution containing the pathogens for analysis later.
Diseases on flowers
Van der Steen decided to use two different methods of analysis: One uses a reagent; the other DNA-analysis. For the first method he uses a lateral flow device (lfd): a double plastic strip with a piece of reagent paper sandwiched between that discolours when a certain fungus or bacteria is present. Prime Diagnostics of Plant Research International supplies such papers containing a reagent that detects various common diseases.
For DNA-analysis he uses a portable PCR-analyser (poly chain reaction). “We used this method two years ago in cooperation with Agis, an Austrian institute for quality in agri- and horticulture to detect fire blight in fruit. We have used them in the Netherlands for detecting bacteria in strawberry and brown rot in cabbage. The results show that bees and bumblebees only carry with them diseases that are present on flowers. This method doesn’t work for leaf diseases, such as brown rot in cabbage.”
Air quality detector
Thinking further ahead Van der Steen sees opportunities for bees to take samples ‘passively’. A honeybee colony spreads itself out over the landscape while searching for food. As well as pollen and nectar they carry ‘other material’ with them to the hive. By taking samples of this and analysing it you get a picture of the diseases that are present in the environment. “The limitation of this method is that it only works with flowers. On the other hand, the possibilities are great. Everything that is spread through the air can be found on the flowers, not only plant diseases, but also bacteria that cause Q-fever, for example,” says the researcher. Van der Steen does see possibilities for using bee colonies as ‘air quality detectors’. “Outside West-Europe, where you don’t find these poles that detect air quality we can use bee colonies as cheap indicators of the environment.”
One of the conditions for using bees and honeybees, whether it is for pollination or disease control, is that the (flying) conditions must be good. Among other things this depends on the greenhouse roof material and the lighting.
Effect of lighting
With the arrival of assimilation lighting the greenhouse conditions, which are already different to outside, are changed even further. Ten years ago, colleague Tjeerd Blacquière who was doing research into the direct effects of high light levels on pollinating insects saw that assimilation lighting affected both these pollinators and the crop as, among other things, the amount of light, duration of light, light spectrum (more heat radiation), the day length and the direction of the light changed. Artificial lighting also altered the vigour of the crop and the day-night rhythm of flowering.
A few years ago Blacquière offered a few suggestions: Set the timing of the lighting so that the opening of the flowers occurs at the most optimal hour for pollination. Close the exit opening of the hives (automatically) well before sunset to prevent (a lot of) workers trying to fly away from the hive in poor light. A few hours of light during the peak in flower opening - during the middle of the day - is sufficient. Research showed that in February around 10 am all sweet pepper flowers had already been stripped of pollen by honeybees.
Use lamps with a better spectrum. Pure red LEDs are probably the most ideal for bees and honeybees. They don’t see red light at all.
Different roofing materials
Blacquière also carried out exploratory research into the impact of using various roofing materials such as glass, polymethylmethacrylate and polycarbonate on the foraging behaviour of bees. In the glass greenhouse the sun was visible as a bright spot in the sky. In the polycarbonate greenhouse the light was scattered into a light arch along the entire firmament. An arch shaped distribution of light was visible to a lesser effect in the polymethylmethacrylate greenhouse.
All the greenhouse roofs allowed PAR-light to enter well. Ultraviolet is hardly transmitted by polycarbonate, partially by glass and completely by polymethylmethacrylate. After introduction to the greenhouse, bees and bumblebees showed normal orientation behaviour under a greenhouse roof of glass and polymethylmethacrylate. Under polycarbonate the bees and bumblebees failed to return to the hive.
In addition to being pollinators, bees and bumblebees are also useful for crop protection. They can carry antagonists to pests and thereby prevent diseases from developing. In addition they can act as air quality detectors because apart from pollen they also carry back bacteria and fungal spores, providing the flying conditions are good.
Text/photos: Marleen Arkesteijn
Manufacturers and horticultural suppliers alike have been expressing increasing interest in the development and market for plant strengtheners. A whole series of products based on substances of a natural origin, from micro-bacteria to hormones and from fungal preparations to seaweed and from algae to fatty acids, are lauded for their resilience-boosting capacities. An overview, however temporary, is presented below.
Our planet’s flora and fauna offer a wide range of substances that are beneficial to crop protection. The members of Artemis develop agents and systems that increase plant resilience to such an extent that diseases and pests simply won’t stand a chance. Artemis is the industry organisation and interest group for biological crop protection. The organisation is composed of manufacturers and suppliers of natural enemies, pollinators and plant protection products of natural origin. The substances (i.e. products) impact a wide range of functions in plant physiology.
According to Alwin Scholten, cultivation advisor and owner of PlantoSys, plant strengtheners can be used in multiple ways. PlantoSys incorporates the plant-based defence protein salicylic acid into its products. Every plant produces this naturally. If the concentration is high enough, the plant starts to produce defence proteins that can block the growth of bacteria, fungi and viruses. ‘Salicylic acid is, in itself, not an antibody. It spurs the plant to produce defence proteins,’ explains Scholten. ‘However, a sufficiently high concentration must be attained in the plant before this will work. This level can be increased by administering salicylic acid to the plant’s leaves (by spraying) or roots. Stimulating the plant’s own immune system through the application of salicylic acid has proved to be highly effective in combating fungus or bacteria-related problems.’ The product appears to be highly effective against biotrophic fungi, such as powdery and downy mildew, Fusarium, rust, fruit rot (Colletotrichum) and Alternaria. It also inhibits the development of spider mites, whiteflies and aphids. Scholten recommends weekly doses as long as problems are anticipated. His product, SalicylPuur, has been approved by the Ctgb as a fertiliser. Other products developed by PlantoSys, with combinations of micro-silver and micro-copper, are marketed likewise. Scholten has noticed a growing interest among horticulturists in plant-strengthening fertilisers. ‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’
‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’
Plant strengtheners are commonly applied to the soil (the substrate) or administered as a fertiliser when watering the plant. The interest expressed by professional growers for soil and crop stimulation agents is growing, but Aly Loes Vellema of ECOstyle bv in Appelscha still has the impression that as long as chemical alternatives are still widely available, the majority prefers to stick to these. Researchers at WUR are also of the opinion that plant strengtheners are not ready to replace crop protection agents, but are a good supplement. ECOstyle focuses on ecologically responsible fertilisers, soil improvers and crop protection agents. Vellema is the supplier of the bio-stimulating soil improver Exsol P, a composite of various types of bacteria. The Bacillus combination has the capacity to free organically bound phosphates and phosphates bound to minerals from the soil, which allows the root system to develop better and the plant to better absorb water and nutrients, thus boosting overall plant resilience. ECOstyle is currently engaged in the development of plant strengthening substances, about which Vellema is not yet ready to share the details.
There are also plant strengtheners on the market that work at photosynthesis level. Pentakeep is a liquid nitrogen fertiliser that is blended with 5-aminolevulinic acid. Administration of this fertiliser causes photosynthesis to be prolonged, and as a result, the production of sugars and dry matter. Cor den Hartog of Pentagrow, importer and distributor of this originally Japanese product, has had over fifteen years of experience with the application of this product in greenhouse horticulture. Tests and studies have demonstrated that Pentakeep enhances vigour and resilience in crops. ‘Research conducted in practice has shown that crops treated with Pentakeep are less susceptible to mildew,’ den Hartog explains. ‘When applied properly, you will have a success rate of 100%.’
5-aminolevulinic acid (5-ALA) occurs naturally in plants, but its production rate depends on the speed of the plant’s metabolism. This metabolism can be accelerated by giving the plant an extra dose of Pentakeep. Plants need 5-aminolevulinic acid to produce chlorophyll. In addition to this, 5-aminolevulinic acid will increase the production of sugars and accelerate the absorption of fertilisers. The result is improved overall growth, higher production rates and stronger plants. Den Hertog confirms that Pentakeep is an NPK fertiliser and regrets that it is not yet 100% biological. The firm aims to bring a biological variant of Pentakeep to the market in the near future.
On the list of the most important disciplines, Koppert Biological Systems occupies the top position with ‘resilient cultivation with NatuGro’. The international market leader of biological crop protection products has placed its resilience activities with EBIC, an international platform for enterprises engaged in the promotion of the bio-stimulants industry in an endeavour to encourage sustainable agriculture and horticulture.
Koppert is convinced that soil resilience is the key to healthy and vigorous plants.
Koppert is convinced that soil resilience is the key to healthy and vigorous plants. With a system that is composed of a diversity of products, soil analyses and expert advice, Koppert offers an all-encompassing approach under the name NatuGro. The products that are included in the NatuGro system are not stand-alone, but form part of an integrated approach: a system that enhances the biodiversity of the cultivation medium and increases the plant’s resistance to disease. A healthy and well-balanced soil life is crucial to this. Pathogenic fungi and bacteria will be inhibited because they are challenged or attacked by various groups of useful organisms in the root environment. One of Koppert’s best-known products is Trianum, a biological plant strengthener containing Trichoderma harzianum T-22 spores. While having a strengthening effect, it also enhances plant resilience in general against a variety of soil fungi. Other products included in the NatuGro system are used in the propagation stage, to stimulate root development and enhance root quality, or to improve photosynthesis.
Other multinationals such as Syngenta, BASF, Bayer and Monsanto are also manifesting themselves on the market of resilience-boosting products. Syngenta is now marketing the biostimulant Hicure and BASF has taken over Becker Underwood, specialised in biological seed treatment. Bayer has submitted an application for the approval of its ‘green’ line of Serenade fungicides and Monsanto is developing various products through its subsidiary BioDirect.
Biobest, established in Lier and a subsidiary of Biobest NV in Belgium, has also developed activities on the market for plant strengthening products. Biobest recently expanded its product range with several items that have a plant-strengthening effect. One of these is Greenstim, about which Biobest claims that it accelerates the transport of specific nutrients. According to this supplier of horticultural products, this has a positive effect on the quality of fruit and perishability. Prestop and PreFeRal are two products that have been introduced into the Biobest range of biological products. Prestop is a biofungicide that combats Botrytis in various crops. Bart Sosef, Director of Biobest Nederland, expects the company’s range of biological products to be expanded in the near future. In relation to this, he has mentioned the fungus Trichoderma, which has a destructive effect on roots.
Biobest is evolving from a manufacturer and supplier of exclusively microbial products into a company that is also active in ‘macrobials’: useful insects and pollinators. Microbials focus more on fungicides that have a direct effect on pests, and in relation to which Sosef has mentioned the biological insecticide PreFeRal. Biobest is seeking collaboration with various partners for the further development of these products, while the marketing emphasis will be placed on guidance and advice. ‘Biobest aims to bring only products to the market that can guarantee the effectiveness they claim,’ explains Sosef.
Text: Tuinbouwteksten.nl/Suzan Crooijmans. Photos: Fotostudio GJ Vlekke, GAPS Photography.